1. Field of Invention
The invention relates to an ink jet type recording apparatus.
2. Description of Related Art
U.S. Pat. Nos. 4,879,568, 4,887,100, and 5,028,936 disclose an ink jet type recording apparatuses that include a shear mode type ink jet head using piezoelectric material. In the shear mode type ink jet head, the volumetric capacity of an ink channel is changed by applying a voltage to the piezoelectric material. When the volumetric capacity of the ink channel is reduced, ink in the ink channel is pressurized, and thereby an ink droplet is ejected from a nozzle. The ejected ink droplet is deposited on a recording medium and, as a result, characters and graphics are printed thereon.
Right after the ejection of ink, ejected ink is divided into two ink droplets, and the two droplets fly individually toward the recording medium. An ink droplet striking the recording medium earlier is called a main droplet and an ink droplet striking the recording medium later is called a satellite droplet.
When a main droplet and a satellite droplet strike the recording medium in an overlapping manner, a large dot is formed thereon. This causes deterioration in print quality when photographic-quality, high-resolution printing is required.
The invention provides an ink jet recording apparatus that can reduce the area of a dot formed on a recording medium to ensure high-resolution and high-quality printing.
In an ink jet apparatus according to the invention, an ejection pulse signal is applied to an actuator so that the actuator changes the volumetric capacity of an ink channel and pressurizes the ink, thereby causing an ink droplet to be ejected from a nozzle to form a dot on a recording medium.
To provide the above ink jet recording apparatus, it is required that the total volume of a main droplet and a satellite droplet ejected in response to a signal for forming a dot is adjusted to 20 pl (picoliters) or less and that the main droplet and the satellite droplet are controlled to be deposited on a recording medium apart from each other. By doing so, the area of a dot formed by each ink droplet is reduced, and thus granularity of a dot is reduced. Accordingly, a high-quality printout can be produced when photographic-quality, high-resolution printing is required.
Specifically, the main droplet and the satellite droplet are adjusted to satisfy X greater than (K1+K2), where X is a center-to-center distance between adjacent dots formed by two main droplets, K1 is a diameter of a dot formed by the main droplet, and K2 is a diameter of a dot formed by the satellite droplet. In addition, ink jet head scanning is controlled such that the satellite droplet strikes the recording medium at a position apart from the main droplet, which has been ejected prior to the satellite droplet, by more than (K1+K2)/2 and less than Xxe2x88x92(K1+K2)/2. Consequently, the two dots are formed by the main and satellite droplets apart from each other without overlapping, and thus granularity of each dot can be reduced.
More specifically, a high-quality printout can be produced by setting V1 in the range of 4.5 to 9.0 m/s and by setting a value obtained by an equation {(D/V2)xe2x88x92D/V1)}xc3x97VS to more than (K1+K2)/2 and less than Xxe2x88x92(K1+K2)/2, where V1 (m/s) is an ejection velocity of the main droplet, V2 (m/s) is an ejection velocity of the satellite droplet, D (m) is a distance between the nozzle and the recording medium, and VS (m/s) is a scanning velocity of the ink jet head relative to the recording medium. Further, in various exemplary embodiments, the value obtained by the equation {(D/V2)xe2x88x92D/V1)}xc3x97VS is set to approximately X/2.
As described above, by controlling the ink droplet ejection velocity, the distance between the nozzle and the recording medium, the ink jet head scanning velocity, and the like, the striking positions of the main and satellite droplets can be controlled. Thus, the distance between the dots formed by the main and satellite droplets can be optimized to reduce the granularity of each dot.
Further, in response to a print command for forming a dot, an ejection pulse signal and an additional pulse signal may be applied to the actuator. The additional pulse signal serves to retrieve a portion of the ink droplet ejected by the ejection pulse signal before the ink droplet leaves the nozzle. By applying the additional pulse signal, the ejected ink volume is reduced. Right after the ejection of ink, ejected ink is divided into a main droplet and a satellite droplet to fly separately. The total volume of the main and satellite droplets is 20 pl or less. In addition, the nozzle is scanned relative to the recording medium such that the satellite droplet strikes the recording medium at a position apart from the main droplet. Accordingly, the area of a dot formed by the main or satellite droplet is reduced and thus granularity of each dot is reduced. As a result, a photographic-quality printout can be excellently reproduced.
Upon the application of an ejection pulse signal to the actuator, the volumetric capacity of the ink channel is increased and a pressure wave is generated in the ink channel. A pulse width of the ejection pulse signal is preferably equal to or odd multiples of a one-way propagation time T of a pressure wave along the ink chamber. When a time corresponding to the width of the ejection pulse has expired, the volumetric capacity of the ink channel starts being reduced from its increased state to a normal state.
In various exemplary embodiments, the width of the additional pulse signal is 0.3T to 0.5T. By setting an interval between a rise time of the ejection pulse signal and a fall time of the additional pulse signal to 0.3T to 0.5T, and by equating a crest value of the ejection pulse signal to a crest value of the additional pulse signal, the main and satellite droplets can be adjusted to substantially the same volume and deposited on the recording medium apart from each other. Thus, granularity of each dot can be further reduced.